1. Field of the Invention
The present invention relates to a ball retainer adapted to be used in a linear bearing of a ball spline, a ball bush or the like for retaining and arraying balls held between a bearing outer cylinder and a bearing shaft and, more particularly, to an improvement in the shape of the ball retainer for circulating the balls smoothly.
2. Description of the Prior Art
The ball retainer of this kind generally known in the prior art is exemplified by a ball retainer 60 of a ball spline, as shown in FIG. 9.
This ball retainer 60 is molded into a generally cylindrical thin shape having a hollow portion 61, in which a spline shaft (although not shown) is loosely fitted. Specifically, the ball retainer 60 is formed in its outer circumference 62 with a plurality of endless ball guide races, each of which is composed of: elongated loaded ball guide races 64 for rolling loaded balls 63 held between a spline outer cylinder 70 and the spline shaft; unloaded ball guide races 66 for loading unloaded balls 65; and ball turning races 67 for connecting the loaded ball guide races 64 and the unloaded ball guide races in communication. Moreover, this ball retainer 60 is fitted for use in the hollow portion of the spline outer cylinder 70 after its endless ball guide races have been arrayed with the loaded balls 63 and the unloaded balls 65.
Considering the assembly efficiency of the ball spline, the ball retainer thus constructed and used is integrally injection-molded of a synthetic resin and is assembled with the spline outer cylinder 70 by inserting it into the hollow portion from one opening of the spline outer cylinder 70.
Incidentially, this spline outer cylinder 70 has its inner circumference divided into: a loaded ball region for holding the loaded balls 63 together with the spline shaft; and a pair of ball scoop regions 68 positioned axially adjacent to the loaded ball region. The loaded ball region is formed axially of the spline outer cylinder 70 with a plurality of ridges 71 for holding the loaded balls 63 between themselves and the spline shaft. On the other hand, the aforementioned ball scoop regions 68 are formed to have such an equal internal diameter that the loaded balls 63 are released in the ball scoop regions 68 from the clearances between the aforementioned ridges 71 and the spline shaft.
In order to fit the integrally molded ball retainer 60 in the hollow portion of the spline outer cylinder 70, therefore, the shape of the outer circumference of the ball retainer 60 has to be configured with the sectional shape of the loaded ball regions formed with the ridges 71. For this reason, the ball retainer 60 is given an axially uniform sectional shape (as shown in FIG. 9).
However, this sectional shape raises the following disadvantages. At first, if the ball retainer 60 has its sectional shape made identical to that of the load ball regions, the aforementioned ball turning races 67 are partially (as indicated at A in FIG. 9) shallowed so much that the rolling runs of the unloaded balls 65 are liable to grow unstable. Since, moreover, the ball turning races 67 correspond to the ball scoop regions 68 of the spline outer cylinder 70, clearances are established between the spline outer cylinder 70 and the ball retainer 60 in the ball scoop regions 68 to make unstable the rolling runs of the unloaded balls 65 in the aforementioned A portions.
As a result, at the time of the high-speed or vertical movements of the spline outer cylinder 70, the unloaded balls 65 are liable to come out of the ball turning races 67 so that they interfere with each other, as shown in FIG. 10, to clog the ball turning races 67. Thus, there rises another problem that the balls cannot circulate any more.